Our NICHD collaborators continue to develop theoretical models of light propagation in tissue, which account for scattering and absorption of light, and predict the spatial profile of the surface intensity of re-emitted and transmitted light. Their models allow for both re-emission of the introduced light and fluorescent light generated by an embedded chromophore, either inherent to or introduced in the tissue. Measurement of a series of surface intensity profiles allows reconstruction of the three-dimensional structure of the tissue using inverse analytical techniques. Likewise, polarization-based models allow interpretation the change of polarization state with scattering changes associated with tissue. Polarization sensitive imaging offers the potential of distinguishing hidden structures developed below the skin surface, such as the collagen network, that can be used to follow the transition from normal to diseased tissue state. Pearson correlation data analysis techniques enable enhancement of images and allow characterization of subsurface structures of biological tissue. One such clinical application being pursued by our NICHD collaborators is colposcopy to assess changes in the cervix that may result from disease or other factors. In partnership with our collaborators we designed both the optical configuration and mechanical layout of this instrument, fabricated, and tested an adaption to a commercial coloposcope that permits these polarization sensitive measurements to be captured and at the same time allows the clinician simultaneous visual and photographic or video assessment of the cervix. This instrument is currently being evaluated in the clinic. Key aspects of this instrumentation are the basis of an ongoing patent application. In a related on-going project to monitor the vasculature of Karposi's sarcoma, a multi-spectral imaging modality is being evaluated to assess changes in morphology due to scattering and simultaneously to use spectral information to assess changes in vasculature function - such as angiogenesis and necrosis - associated with the different treatment modalities being pursued in the clinic. The current instrumentation is based on sequential change of filtration that is time consuming, subject to sequential access, and limited in its ability to provide for variable intensity of illumination. We have recently obtained a commercial near-infra-red illumination system that we will adapt and introduce as a replacement for the current light source. It will allow real time analysis for assessment of clinical conditions by providing with millisecond resolution random access to different wavelengths of light (600nm to 1100nm), modification of the bandwidth and intensity of illumination, and allow for exposure times from sub-millisecond to "infinite". To date, this near ir source is operational and upon receipt of the software LabView drivers, appropriate illumination parameters will be programmed into the instrument prior to installation and evaluation in the clinic. It is expected this will provide more complete clinic data and provide a significant improvement for the patient in terms of time taken to perform the necessary measurements. In another collaboration with the NICHD group, we are pursuing building a small, portable, and wearable system that uses near infrared light for brain imaging. It is envisaged that the necessary sources, detectors, and associated electronic circuits for processing, transmitting and receiving data can be mounted within a helmet. The optical source couples light into the brain and the resulting light after transmission through the diffusive brain tissue is collected by the receivers, and the processed data will enable an evaluation of the hemodynamic response. To enable this aspect of the project, we have recently ordered prototype dual-wavelength (780nm and 850nm) optrodes that we will integrate into the package worn by the patient. It is estimated that the final unit will be less than 4cm x 4cm. We continue our interest in the use of near infrared upconverters for use in these studies (we are also pursuing the use of these as luminescent labels - see "Instrumentation" annual report). Identification of deeper structures within the tissue is possible by extending to the near infra-red region of the spectrum and by the use of novel infrared compounds to act as probes localized at desired sites within the tissue.